An aluminum coating may endow a substrate with certain benefits including corrosion resistance, oxidation resistance, enhanced appearance, wear resistance, improved performance, etc. There are several drawbacks to conventional aluminum deposition techniques such as chemical vapor deposition, pack cementation, and electroplating. Conventional aluminum electroplating is complex, costly, performed at high temperatures, and/or requires the use of flammable solvents and pyrophoric compounds that decompose, evaporate, and are oxygen-sensitive, necessitating costly specialized equipment and presenting serious operational challenges to a commercial production facility.
Ionic liquids with aluminum salts (“ionic liquid aluminum electroplating solutions”) have also been used to electroplate aluminum on superalloy substrates and non-superalloy substrates (e.g., steel). While such ionic liquid aluminum electroplating solutions are known to produce a high purity (greater than about 99.5%), dense coating, the coating may include dendrites (a crystal or crystalline mass with a branching, treelike structure) and/or nodules (small rounded lumps of matter distinct from their surroundings) (collectively referred to herein as “coating defects”), resulting in less than optimal coating uniformity and possible coating spallation, particularly when the coating thickness is greater than 25 micrometers (μm). The addition of conventional electroplating bath additives known as surface modifiers (also known as leveling agents) to the conventional ionic liquid aluminum electroplating solution has not eliminate these problems.
Accordingly, it is desirable to provide effective surface modifiers for ionic liquid aluminum electroplating solutions, processes for electroplating aluminum therefrom, and methods for producing an aluminum coating using the same. The surface modifier increases throwing power and inhibits coating defects in the aluminum coating produced from the ionic liquid aluminum electroplating solution containing the surface modifier. The surface modifier also provides better coating uniformity with improved surface morphology and reduced coating defects, longer plating bath life and a higher plating rate relative to electroplating with conventional ionic liquid aluminum electroplating solutions.